Mobile communication systems and devices are in widespread use in most metropolitan regions of the world. In many places, wireless communications service is even being deployed where there is no wired communication service, due to the lower cost of infrastructure equipment. As mobile communications technology has matured, various features and additional services have been added beyond simply circuit-switch radiotelephony. Data services have been added so that subscribers can access information over public wide area networks and wireless local area networks. As mobile data networks have matured, there has been interest in carrying real-time information such as voice over them. Voice over Internet Protocol (VoIP) has been deployed with success at fixed data terminals, such as personal computers, and interest in using VoIP over mobile data networks is growing.
Interest has been focused on increasing the information throughput to and from subscriber devices over wide area wireless mobile data networks. One technology that has garnered interest for provided high quality, high capacity service is that specified by the IEEE 802.16e specifications, known as the Worldwide Interoperability for Microwave Access, or “WiMAX.” The relatively high data capacity of this protocol allows for VoIP operation as it can reliably transmit data with a quality of service needed for time-sensitive applications.
To facilitate power saving operation, the WiMAX protocol allows a mobile communication device to establish a VoIP call with a power save mode. During the power save mode, the framing may be configured to alternate between an active interval and a sleep interval. During the active interval, the mobile communication device receives data from a serving base station, and transmits data to the serving base station. The data includes both VoIP data and any other data for other applications that may be running on the mobile communication device. During the sleep interval, the mobile communication device places the radio modem into a low power or sleep state to reduce average power consumption.
However, the mobile communication device must periodically conduct some mobility management functions, including scanning neighbor base stations. Due to the time-sensitive nature of the data being carried during the active interval, the mobile communication device must remain tuned to the present base station. Thus, scanning must be done outside of the active interval. So, in scan mode, what was the sleep interval during power save mode becomes a scan interval during scan mode. During the scan interval the mobile communication device tunes away from the present base station to receive signals from other base stations within reception range of the mobile communication device. Typically the serving base station transmits a neighbor list to the mobile communication device during, or shortly after the affiliation or handover process when the base station becomes the present serving base station.
Under the present implementation of the WiMAX protocol, which supports both sleep mode and scan mode as described so far, a mobile communication device must transition from one mode to the other, and vice versa. To make a transition, the mobile communication device transmits a request to the base station. Upon transmitting the request, however, the mobile communication device is deactivated from power save mode, and must have the radio modem on until the start of scan mode. As defined now, the transition period is at least 8 frames long. Thus, to transition to and from scan mode, the mobile communication device will have two periods of at least 8 frames each where it is not scanning, nor in power save mode. It is therefore desirable to eliminate the transition time to decrease the power consumption of the mobile communication device.